Hybrid Darlington amplifiers are known in which a field effect transistor functions as an input amplifying stage and a bipolar transistor functions as a second amplification stage for providing a low output impedance with a high degree of amplification of an input signal applied to the input amplification stage. See U.S. Pat. Nos. 4,303,841, 4,480,201, 4,547,686, 4,590,395 and U.S. Pat. No. 4,604,535.
U.S. Pat. No. 4,547,686 discloses an amplifier which uses a Zener diode to discharge the capacitance of field effect transistor Q.sub.2 during turnoff. See column 2, lines 18-26 and column 3, lines 34-45.
U.S. Pat. No. 4,590,395 discloses as "prior art" in FIG. 3 a shunt field effect transistor 72 which removes minority carriers in a bipolar transistor 76 to promote turnoff. See column 3, lines 37-50. Furthermore, FIG. 4 of U.S. Pat. No. 4,590,395 discloses a Zener diode coupling the gate and base electrodes of a hybrid Darlington amplifier together to promote high speed turnoff. See column 4, lines 19-38.
U.S. Pat. No. 4,604,535 discloses a two-stage amplifier using a junction field effect transistor to short-circuit the base to the emitter in an output stage bipolar transistor to eliminate the storage of charge in the base-to-emitter junction to promote high speed turnoff. See column 5, lines 21-28.
U.S. Pat. No. 4,028,561 discloses that the turn-off speed of a Darlington amplifier comprised of bipolar transistors may be enhanced by a third transistor. Carriers stored in the base and collector of the output bipolar transistor are discharged through the base emitter path of the third transistor which is coupled between the collector and emitter of the output bipolar transistor and the base and collector of the first input transistor. See column 3, lines 25-55.
U.S. Pat. No. 4,423,341 discloses that the turn-off speed of a field effect transistor is dependent upon the rate at which the gate capacitance can be discharged. See column 6, lines 9-32.
U.S. Pat. No. 4,492,883 discloses that the turn-off speed of a field effect transistor may be enhanced by the use of a junction field effect transistor to drain off residual charge stored in the gate-to-source capacitance of the field effect transistor. See column 1, lines 10-47.
U.S. Pat. No. 4,481,434 discloses that the turn-off speed of a field effect transistor may be enhanced by shorting the gate and source together by a bipolar transistor operated as a regenerative switch. See column 1, lines 32-38 and column 2, lines 21-38.
U.S. Pat. No. 4,500,801 discloses that the turn-off speed of a field effect transistor may be enhanced by a non-regenerative bipolar transistor which shorts the gate and source together. See column 1, lines 32-36.